Pressure atomizing burners or liquid spray heads have been heretofore used to atomize liquid in the various fields of art as mentioned above. The term "liquid" herein used is intended to mean not only liquid but also various liquid materials such as solution, suspension and the like. Injection nozzles used on such spray burners and liquid atomizers are adapted to atomize the liquid by virtue of the shearing action between the liquid discharged through the nozzles and the ambient air (atmospheric air). Accordingly, increased pressure under which the liquid was supplied was required to achieve atomization of the liquid, resulting in requiring complicated and large-sized liquid supplying facility such as pumps, piping and the like.
Furthermore, regulation of the flow rate of injection was effected by varying either the pressure under which to deliver supply liquid or the area of the nozzle outlet opening. However, the former method provided poor liquid atomization at a low flow rate (under a low pressure), as a remedy for which air or steam was additionally used on medium or large-sized boilers to aid in atomization of liquid, requiring more and more complicated and enlarged apparatus. On the other hand, the latter method required an extremely intricate construction of nozzle which was troublesome to control and maintain.
In order to overcome the drawbacks to such prior art injection nozzles, attempts have been made to impart ultrasonic waves to liquid material as it is injected out through the jet of the injection nozzle under pressure.
However, the conventional ultrasonic liquid injecting nozzle had so small capacity for spraying that it was unsuitable for use as such injection nozzle as described above which required a large amount of atomized liquid.
As a result of extensive researches and experiments conducted on the ultrasonic liquid atomizing mechanism and the configuration of the ultrasonic vibrating element in an attempt to accomplish atomization of a large amount of liquid, the present inventors have discovered that it is possible to atomize a large quantity of liquid by providing an ultrasonic vibrating element formed at its end with an edged portion along which liquid may be delivered in a film form, and have proposed an ultrasonic injection nozzle based on said concept as disclosed in Japanese Patent Application No. 59-77572.
Such ultrasonic atomizing apparatus will be briefly described with reference to FIG. 4. The apparatus is illustrated in FIG. 4 as a fuel injection valve 10 for use with a gas turbine engine. The valve 10 includes a generally cylindrical elongated valve body 8 having a central bore 6 extending through the center thereof. Disposed extending through the central bore 6 is a vibrating element 1 which includes an upper body portion 1a, an elongated cylindrical vibrator shank 1b having a diameter smaller than that of the body portion 1a, and a transition portion 1c connecting the body portion 1a and the shank 1b. The body portion 1a has an enlarged diameter flange 1d which is attached to the valve body 8 by a shoulder 12 formed in the upper end of the valve body and an annular vibrator retainer 14 fastened to the upper end face of the valve body by bolts (not shown).
The forward end of the vibrating element 1, that is, the forward end of the shank 1b is formed with an edged portion 2 the details of which are shown in FIG. 3. The valve body 8 is formed through its lower portion with one or more supply passages 4 for feeding said edged portion 2 with fuel. The fuel inlet port 16 of the supply passage 4 is fed with liquid fuel through an exterior supply line (not shown) from an external source of fuel (not shown). The flow and flow rate of fuel are controlled by a supply valve (not shown) disposed in the exterior supply line.
With the construction described above, the vibrating element 1 is continuously vibrated by an ultrasonic generator 100 operatively connected to the body portion 1a. Liquid fuel is thus supplied through the exterior line, the supply valve and the supply passage 4 to the edged portion 2 where the fuel is atomized and discharged out.
As illustrated in FIG. 3, the edged portion 2 of the prior art vibrating element 1 comprises a plurality of (five in FIG. 3) annular concentric steps having progressively reduced diameters.
More specifically, with the construction described above, as liquid which is fuel in the illustrated example is passed to the edged portion 2, the stream of fuel is severed and atomized at each edge due to the vertical vibrations imparted to the vibrating element 1. Fuel is first partially atomized at the edge A of the first step, and the excess portion of the fuel which has not been handled at the first step edge A is fed further through the second step edge B, third step edge C and so on to be handled thereby. It is to be understood that at a higher flow rate of fuel a larger effective area is required for atomization, requiring a greater number of step edges. At a lower flow rate, however, a smaller number of steps are required before the atomization of fuel is completed. With the vibrating element 1 as described above, the number of steps required will vary with changes in the flow rate so as to insure generally uniform conditions such as the thickness of liquid film at the location of each step where the atomization takes place, resulting in uniform particle size of the droplets being atomized. In addition, the vibrating element of this type accommodates a full range of flow rates usually required for pulverization, so that atomization of various types of liquid material may be accomplished, whether it may be on an intermittent basis or a continuous basis.
The geometry of the edged portion of the vibrating element 1 such as the shape, height (h) and width of each step of the edged portion of the vibrating element shown in FIG. 3 was such that the edge of each step might act to reduce the liquid to a thin film and dam the liquid flow.
However, with the vibrating element 1 having such configuration, it has been found that in some instances an excessively large pool of liquid S may be formed around the vibrating element above the edge A of the first step as shown in FIG. 3, whereby the supply liquid from the supply passage 4 may not consistently be supplied to the edges B, C, D and E of the second to fifth steps with the result that a desired amount of atomization may not be accomplished. Such phenomenon must be avoided by all means in injection valves for continuous combustion or automobiles.